Pump



May 5, 1942. w. w. HECKERT PUMP Filed July 12, 1.940

Patented May 5, 1942 PUMP Winfield Walter Heckert, Wilmington, Del., as-

Signor to E. I. du Pont de Nemours & Company, Wilmington, Del., acorporation of Delaware Application July 12, 1940, Serial No. 345,119

1 Claim.

This invention relates to an improvement in liquid propelling gearpumps. It relates furthermore to an improved method of uniformlymetering bubble-containing compositions. It relates particularly to gearpumps of the type commonly used in metering a filament-forming solutionto a spinneret in the production of artificial filaments. The inventionhas particular utility in the spinning of molten organicfilament-forming compositions which are subject to bubble formation,whether this formation is a result of the method used for melting or isa result of decomposition of the compositions in their molten state.

In the copending application of George De- Witt Graves, Serial No.232,314, filed September 29, 1938, there is disclosed a method ofproducing continuous structures. such as filaments, yarns, ribbons andthe like of very uniform denier or gauge, from compositions subject tobubble formation, by a process wherein the filmor filament-formingcomposition is subjected to sumcient pressure to dissolve the bubbles inthe composition and then this bubble-free melt is metered, while beingmaintained under pressure, to an extrusion device such as a spinneret.This can be accomplished, for example, by the use of two pumps connectedin series, the first subjecting the filmor filament-forming compositionto pressure and delivering the bubble-free composition so produced to asecond pump, which meters the bubble-free composition to a suitableextrusion device.

The use of two pumps will function to meter a substantially bubble-freecomposition to the extrusiondevice but presents mechanical problems,especially at the high temperatures involved in melt extrusion. Pumpwear, maintenance, provisions for synchronous drives, etc., make them'expensive and tend to make the extrusion apparatus cumbersome.Likewise, the use of two pumps increases the amount of film! orfilamentforming compositions which must be maintained in the moltenstate and hence prolongs its exposure to conditions promotingdecomposition.

It is, therefore, an object of this invention to provide an improvedmethod and apparatus for the production of structures from fllmorfilament-forming compositions which contain bubbles under the conditionsof extrusion.

It is another object of this invention to provide an improved method andapparatus for the "elimination of bubbles from fllmand filamentformingcompositions and for metering the resulting bubble-free compositions toa structureforming device.

Other objects of this invention will appear hereinafter.

The objects of this invention may be accomplished, in general, by usinga gear pump so designed that the entrapped composition between themeshing gears is forced, through a passageway in the side walls of thepump, to the composition being propelled, or pumped, by the gears so asto dissolve bubbles present in the propelled molten composition beforethe latter is forced into the pump outlet.

More particularly, the composition under pressure may be led by means ofgrooves provided in the pump side walls to a position adjacent to theteeth of the gears in their path of travel from the inlet to the outletports. There the composition exerts pressure on the composition beingpropelled by the gear-teeth, and by this pressure bubbles in thecomposition being propelled are caused to dissolve.

The invention will be more easily understood by reference to thefollowing detailed description when taken in connection with the accom--a;

panying illustration, in which:

Figure 1 is a cross section on the plane of the I axes of the gears of agear pump constructed in accordance with the invention.

Figure 2 is an elevational view of the inside face of one side plate ofthe gear pump shown in Figure 1.

Figure 3 is an elevational view of the center plate and gears of thepump shown in Figure 1.

Figure 4 is an elevational view of the inside face of the other sideplate of the pump shown in Figure 1.

Figure 5 is an enlarged diagrammatic elevational view of a section ofthe gears projected on a section of the side plate shown in Figure 2.

Figure 6 is a cross-sectional view taken along the line 6-6 of Figure 2.

Figure 7 is a cross-sectional view taken along the line 1-1 of Figure 4.

Figure 8 is an elevational view of the inside face of a modified form ofside plate.

Referring to Figures 1 to 7 of the drawing, reference numeral lldesignates the rear side plate of the gear pump and numerals l3 and I5designate respectively the center plate and front side plate. The threeplates are held together by means of suitable bolts or screws (notshown). A pair of meshing gears I1 and i9 are operatively positionedwithin the center plate I3 and between side plates H and IS. The gears Hand I8 are mounted respectively on drive shafts 2| and 23. The geardrive shafts 2| and 23 are journaled in the side plates II and I5, theshaft 2| being positioned in openings 3'6 and 31a of the respective rearand front plates, and shaft 23 being positioned in openings 39 and 39arespectively of said rear and front plates.

The rear side plate II is provided with an inlet opening 33 and anoutlet opening 35 for the liquid. Plate II is furthermore provided witharcuate grooves 25 and 29, as well as connecting grooves 21 and 3|, thelatter grooves respectively connecting arcuate grooves 25 and 29 withdepressions 26 and 28 which are positioned adjacent the points ofinter-meshing of the teeth of the gears I1 and I9 (see Figure Theseveral grooves are positioned on the inside face of the plate as isclearly shown in Figure l. The arcuate grooves 25 and 29 are concentricwith the shafts 2| and 23 and are positioned to overlie a number ofgear-teeth between the inlet 33 and the outlet 35. A small groove 4 I,connecting with the inlet opening 33, is also provided on the insideface of plate H (see Figures 2 and 6). The purpose of this groove 4| isto bring grooves 2'! and 3| sufliciently close to inlet opening 33 toinsure that leakage between the said plate II and the center plate, dueto excess pressure on the liquid in grooves 21 and 3|, will flow to theinlet opening 33 rather than the outlet opening 35. The front side plateI5 is provided, on the inside face thereof with arcuate grooves 25a and29a and connecting grooves 21a and 3|a. which are mirror images of thegrooves in the rear side plate II. Plate I5 is also provided with asmall circular groove 4'! which is positioned adjacent the point wherethe gears are unmeshing. Groove 41 functions to relieve any vacuumcreated by the unmeshing gears.

The center plate I 3 contains two circular openings 5| and 53 into whichthe gears I1 and I9 fit with a minimum of clearance yet permitting freerotation of the gears. The gears I1 and I9 are shown mounted on theirrespective shafts 2| and 23. These are designed to be driven in thedirection shown by the arrows. The enlarged recessed spaces 43 and 45connect with the inlet 33 and outlet 35 respectively and serve as liquidconveying openings for the gears.

The mechanism whereby the filament-forming composition is entrappedbetween the gears, subjected to pressure, and fed into the grooves inthe side plates is shown more clearly in Figure 5. The gears I1 and I9at the point where the teeth engage and entrap the liquid overlie thedepressions 26 and 23 at the ends of grooves 21 and 3|. The tooth 10 ofgear I9 has just reached a position relative to the teeth I2 and 14 ofgear I'I where it has completely entrapped the filament-formingcomposition in the space 15 between the teeth 12 and I4 and is beginningto subject it to pressure. The depression at the end of groove 3| in therear side plate II is so located that the entrapped filamentformingcomposition is forced into the groove 3|. A similar action occurssimultaneously at the corresponding depression 28a at the end of thegroove 3|a in the front side plate I5 (not shown). Simultaneously, thetooth 14, as shown, has just completed forcingthe filament-formingcomposition, entrapped between teeth 10 and 18, into the depression 25at the end of groove 21. The tooth I2 is shown entering the spacebetween teeth and I0 and will force the entrapped I composition intodepression 26 and groove 21,

and, of course, the oppositely disposed depression 26a and groove 21a offront side plate, not shown in Figure 5. The composition forced intogrooves 21 and 3|, and 21a and 3m will be forced into the respectivearcuate grooves 25 and 295, and 25a and 29a, and thence into the spacesbetween the gear-teeth to which the arcuate grooves are contiguous. Theadditional pressure imparted to the composition being propelled from theinlet to the outlet opening will cause a dissolution of any bubbleswhich may be contained therein.

It is usually preferred to so design the gearteeth that a somewhatlarger quantity of filament-forming composition is entrapped and fedthrough the grooves than is theoretically required, thus insuring thatthe teeth delivering the bubble-free filament-forming composition arecompletely filled. This is especially desirable since the rate ofbubble-formation is often inconstant and hence the bubble content of thefilament-forming composition is non-uniform so that provision must bemade to dissolve the maximum quantity of bubbles present at any time.For this reason, provision must be made for the release of .the excessquantity of this material. In general, it is preferred that this be fedback to the inlet of the pump, especially if the quantity isnon-uniform, since if fed to the outlet, it would defeat the purpose ofuniform metering. This release can be accomplished in a number of ways.In some cases, the natural slip between the gear-teeth and the centerplate I3 will accomplish it or the clearance may be increased slightlyto increase the slip. Likewise, slip between the faces of the gears andside plates II and I5 will permit return of the excess to the inlet.When this occurs, it is important to in-- sure either by location of theinlet and outlet ports relative to the grooves and/or by supplementarygrooves or recesses, that the resistance to slip between the grooves andthe inlet port at their closest point is less than that between thegrooves and the outlet port at their closest point. It will be notedthat in Figure 2 the inlet port 33 is located closer to the grooves 21and 3| than is the outlet port 35. The return of the excess to the inletport may be further insured by an enlargement 4| of the inlet port asshown in Figure 2. This enlargement 4| need be only recessed in theplate II; however, it may be recessed in both side plates II and I3.

The presence of this enlargement shortens the distance of closestapproach of the connecting grooves 21 and 3| to the inlet port andthereby facilitates escape of excess composition to the inlet portacross the face of the gears, between them and the plates II and/or I5.If desired, small passages may be recessed in the plate giving directcommunication between the grooves carrying filament-forming compositionto the teeth and the inlet port, the width and depth of the recessedpassages being determined to maintain the desired pressure.

Although the length of the arcuate grooves 25 and 29 is shown to beapproximately in the drawing, many modifications of this length arepossible in the scope of the invention. The criteria for selection ofthe proper length are: the concentration of bubbles present in thecomposition under the conditions of extrusion, the viscosity of thecomposition extruded and the precision of metering desired. As will bereadily appreciated by one skilled in the art, one factor to be takeninto account in determining the length of the grooves is the length oftime the composition must be subjected to pressure to effect solution. Alimit to the length of the grooves is imposed by the necessity ofproviding a sufficient distance between the end of a groove and theoutlet port to prevent slip of the composition from the groove to theoutlet. Such a slip would destroy the metering feature of the pump ofthis invention. Another limit to the length of the grooves is thenecessity for provision of an ungrooved or only slightly grooved spacebetween the inlet port and the grooves as has been indicated above indiscussion of release of excess composition from the grooves. It ispreferred that the arcuate grooves be sufficiently long to overlie aplurality of gear-teeth.

Many modifications of the shape of the grooves are possible. Forexample, in Figure 8 the connecting grooves 21 and 3| are extended toJoin each other by the groove 34. Similarly, while the grooves have beenshown in both the front and rear plates they may be placed in only oneplate if desired. Obviously, other modified constructions for return ofexcess composition to the inlet opening can be devised. In Figure 8,recessions are shown at 35 in addition to that shown at ll to facilitatethis action.

Although this pump is especially adapted for the melt spinning ofsynthetic linear polyamides, it is obviously applicable to the meltspinning of any organic filament-forming composition, which is subjectto the formation of bubbles, for any reason, under the conditions justprior to and during the spinning thereof provided the gases redissolveunder pressure and the decomposition is slow enough to permit meteringbefore sufficient gases are formed to exceed the solubility under theconditions of temperature and pressure. As examples of suchfilamentforming compositions in which bubble-formation may be present,the following may be mentioned: Synthetic linear polyamides, that is,synthetic linear polymers containing CONH units in the linear chain;synthetic linear polymers such as polyesters, polyethers, polyacetalsand mixed polyester-polyamides such as may be prepared by condensationreactions as described in U. S.'

Patent No. 2,071,250 may also present problems of bubble-formation whichcan be remedied by the process of the present invention. Other types ofsynthetic polymers such as ethylene Polymers, vinyl polymers,polystyrene and polyacrylic acid derivatives may also be spun withadvantage, in accordance with the present invention.

The filament-forming material used in accordance with the presentinvention may contain modifying agents, e. g., luster-modifying agents,plasticizers, pigments and dyes, antioxidants, resins, etc. The presentinvention may also be used to advantage in extruding filmorfilamentforming compositions in which the bubble formation is caused bythe presence of a modifying a ent.

Although this pump has been described with reference to the extrusion offilmor filamentforming compositions, it is also applicable to themetering of bubble-free compositions in the spinning of bristles and thecoatin of wire, etc.

This pump may also be used to advantage in the spinning or extrusion ofother types of filament-forming solutions, for example, cellulosexanthate or other-cellulose derivative solutions, when gas bubblespresent a problem. Also, these solutions may be metered advantageouslyby this pump if they contain bubbles caused by the presence of modifyingagents or from any other cause.

This pump also finds application in the pumping of liquids at or neartheir boiling points so that liquid only is metered without the presenceof gases. In this connection, this pump has utility as a dispensingdevice. This pump may also be used to meter liquids undergoingdecomposition with the evolution of gases.

By the practice of this invention it is possible to produce structuresof very uniform properties particularly yarns of very uniform denierfrom filament-forming compositions having a tendency to form bubblesduring the extrusion thereof. This is accomplished by a simpleinexpensive and compact apparatus the maintenance of which is low andthe power consumption small. The uses of this apparatus are particularlyadvantageous in the spinning of molten composition. An importantadvantage in melt spinning is the fact that less work is done on themolten material than with compression between two pumps thereby reducingthe temperature of the pump block and permitting the use of highertemperatures in melting the solid filament-forming composition withoutraising the temperature of the pump block to a temperature which wouldpromote too rapid decomposition.

Gear pumps constructed according to this invention tend to show lesswear in use than previously known gear pumps. This is due to theequalization of pressures of the liquid being metered over a largesegment of the gear-teeth and to the fact that in this pump pressure ofthe composition on both sides of the gear arbors is balanced.

Obviously many changes and modifications can be made in theabove-described structures without departing from the nature and spiritof the present invention; it is therefore to be understood that theinvention is not limited to the specific structures above-describedexcept as set forth in the following claim.

I claim:

In a liquid propelling gear pump of the type in which a pair of meshinggears, housed in a center plate and between side plates, propels theliquid from an inlet opening to an outlet opening in cooperation withthe peripheral surface of the center plate surrounding said gears, anarouate groove in at least one of said side plates, said groovepositioned to overlie a plurality of gearteeth engaged in propellingliquid from the inlet opening to the outlet opening, a second groove insaid side plate, said second groove positioned between said arcuategroove and a point overlying the meshing gear-teeth, and groove means insaid side plate projecting only from said inlet opening towards, but notin direct connection with, said second groove whereby to induce leakageto said inlet opening upon reaching excessive pressure.

wmrmn WALTER nncxna'r,

